1. Field of Invention
This invention relates generally to analgesics to relieve pain in living organisms both human and animal, and more particularly to a periodic pulsed heat technique which induces analgesic effects in the organisms without the use of drugs.
2. Status of Prior Art
The term analgesic refers to a drug whose chemical structure and physiological effects are such that when the drug is administered, it then acts to relieve pain. To qualify as an analgesic, the drug must reduce or abolish pain without, however, impairing consciousness, causing mental confusion or otherwise deranging the nervous system. Thus a drug which renders the patient unconscious is not an analgesic, but an anesthetic, even though it abolishes pain.
One well-known class of analgesics are the narcotic alkaloids. The oldest and best known are opium and morphine, its most active alkaloid. Also derived from opium is codeine. A person who takes opium or its derivatives for a prolonged period needs and tolerates larger and larger doses to obtain the desired effect, and therefore, becomes habituated. Should the use of the drug be then stopped, highly disagreeable withdrawal symptoms are experienced. Narcotic alkaloids are all potentially addictive, and an addict will often go to great lengths to obtain the narcotic to avoid withdrawal symptoms. Among non-narcotic analgesic drugs are the salicylates, such as aspirin. But these are far less effective in reducing pain than morphine and synthetic opiods.
Endorphins are manufactured within the central nervous system and share with narcotic alkaloids the ability to relieve pain. Endorphins function as neuromodulators in a system descending from the brain through the spinal cord which counteract painful impulses coming from the periphery toward the brain.
The term "endorphin" is an elision of ENDOgenous and moRPHINe. "Endogenous" means produced within the body, as distinguished from "exogenous" which means produced outside of the body. The term endorphin is now generic to a family of endogenous opiates that include leucine enkephalin, and alpha, beta, gamma and delta endorphin; as well as a growing number of synthetic compounds. The reason narcotic analgesic drugs are effective is that they mimic the actions of natural endorphins by occupying stereospecific opiate receptors in the brain, the spinal cord and the gut, normally occupied by endorphins.
For purposes of classification, drugs which have analgesic properties fall into the exogenous class, while internallygenerated endorphins fall into the endogenous class of analgesics. The problem with exogenous analgesics is that these drugs have adverse side effects, especially if used to excess. Indeed, the more powerful the drug, the greater its undesirable side effects. Yet these drugs are often prescribed, for internally-produced endorphins are inadequate to relieve severely painful conditions. The human brain which governs the generation of endorphins is dedicated to the survival of the body it occupies, and the brain, therefore, manipulates the production of endorphins toward this end. Thus when a soldier in battle is slashed by a bayonet, though bleeding profusely, he then experiences little pain, for the pain sensation is blocked by endorphins. This makes it possible for the soldier to continue fighting, for it is only later that intense and disabling pain is experienced.
However, pain control is but one function of the central nervous system composed of the brain and the spinal cord which together control and correlate body actions and reactions. The central nervous system operates in conjunction with a network of peripheral nerves whose sensory or afferent nerves convey signals via the spinal cord to the brain. These signals stimulate the brain to act in a manner appropriate to the information it receives from the internal sensors.
Every sensation experienced by a living organism depends on impulses excited by stimulation of receptors. Thus heat is detected by heat-sensitive receptors in the skin, the electrochemical impulses or signals emitted by the receptors being delivered by afferent nerve fibers in the peripheral nervous system via the spinal cord to the brain. Other receptors in the skin and those distributed throughout tissue underlying the skin and elsewhere in the body, sense touch and other stimuli, but these are not the concern of the present invention whose interest is limited to thermal receptors and the signals produced thereby.
When in the example given above, our soldier is slashed, the nervous reaction not only stimulates the brain into producing endorphins to reduce the sensation of pain, but also to cause swelling near the site of the wound. This swelling clears the way for emergency measures which include phagocytes produced by the immune system that pour into the wounded region to consume bacteria, viruses and dead cells, and thereby promote the healing process.
The thermal receptors in the skin that signal the brain are responsive to the temperature of the sensed heat regardless of the extent of tissue damage produced by the heat to which the human organism is exposed. Thus if the heat to which the body is exposed produces a severe burn and the receptors then detect a temperature of say 140.degree. F., the signals produced by the receptors will be the same as when pulsed-heat is applied to the body which results in a temperature of 140.degree. F., yet does not give rise to a burn. In either case, the brain receives the same stimuli from the sensors, and the brain will take the same emergency measures, including the production of endorphins to reduce the sensation of pain.
In a pulsed-heat technique in accordance with the invention, in order to produce pulsed-heat having an analgesic effect comparable to that produced by exogenous drug analgesics, but without adverse side effects, use is preferably made of a pulsed-heat applicator of the type disclosed in our 1992 U.S. Pat. No. 5,107,832 entitled "Universal Thermotherapy Technique."
The applicator disclosed in our patent includes a casing dome whose open base is maintained in spaced relation to a skin area of a patient to define an air flow zone therebetween. Coaxially mounted at an intermediate position within the dome is a motor-driven fan which creates a negative pressure region in the dome above the fan and a positive pressure region therebelow, whereby air drawn from the negative pressure region is propelled into the positive pressure region from which it is discharged into the air flow zone. From this zone, the air is returned to the negative pressure region, thereby creating a circulatory flow loop minimizing the discharge of air into the atmosphere outside the flow zone.
Mounted coaxially within the dome in the negative pressure region is an electric heater ring formed by a helical resistance coil. When the heater ring is energized, the air circulating in the loop passes through the coil and is raised in temperature to a level that is a function of fan velocity, the higher the velocity the lower the temperature level. An electronic control unit associated with the fan motor acts to periodically change the fan velocity from a predetermined high value at which the resultant temperature level of the air in the flow zone is then at a base level above ambient but somewhat below the sensitivity threshold of the patient being treated, to a predetermined low velocity value at which the resultant temperature level is reaised above the base level to create high temperature heat pulses whose peaks are well above the sensitivity threshold.
A pulsed-heat applicator of the type disclosed in our prior patent is adapted to apply heat to a problem region underlying the skin surface without however raising the temperature at the surface of the skin to a level that cannot be tolerated by the patient. The difficulty heretofore experienced in effectively applying heat to a patient is that when the heat is transferred inwardly through living tissue to the problem region, then if the heat applied to the skin surface for this purpose is within a tolerable temperature range and does not burn the skin, not enough heat energy is transferred to the site being treated to afford beneficial therapeutic effects. This drawback is overcome by the applicator disclosed in our prior patent in which the applied heat is in the form of periodic high-temperature pulses.
The duty cycle of these pulses is such as to allow for internal heat transfer to take place in the tissue below the exposed skin area of the patient in the intervals between pulses to an extent preventing an excessive rise in temperature at the skin surface whereby the patient gains the benefit of high heat energy treatment without discomfort or injury.
The concern of the present invention is not with the application of elevated heat to an internal problem region of the body, but with the application of heat to a skin area of the body to excite the thermal receptors in the skin to produce signals stimulating the brain to produce endorphins having analgesic effects. While the application of pulsed heat to the skin will inevitably result in the transfer of heat to regions underlying the skin, the extent to which these region is heated is an incidental effect. In the present invention, no more heat is applied to the skin than is necessary to induce analgesic effects.